1. Field of the Invention
The invention relates to non-invasive positive pressure mechanical ventilation, and to methods and apparatus for treatment of sleep disordered breathing.
2. Description of Related Art
The shape of the inspiratory portion of the flow-time curve for a breath is recognised as being indicative of the patency of the upper airway of a person. A normal breath is generally “round”. “flattening” of the inspiratory portion of the respiratory flow curve has been recognised as an indication of upper airway instability, resistance or partial obstruction. See FIG. 1. This phenomenon has been used to control a nasal Continuous Positive Airway Pressure (CPAP) device for treating Obstructive Sleep Apnea (OSA). See U.S. Pat. No. 5,704,345 (Michael Berthon-Jones). The contents of this patent are hereby expressly incorporated by cross-reference. The '345 patent describes a method and apparatus for resolving flow limitation by increasing the CPAP pressure provided to the patient until the shape of the flow curve becomes suitably rounded. In some cases, during non-invasive positive pressure mechanical ventilation, increasing the end-expiratory pressure alone may not resolve the upper airway obstruction, resistance or instability. Increasing End Expiratory Pressure (EEP) may lead to a decrease in patient comfort as the result of the increase in both Expiratory Positive Airway Pressure (EPAP) and Inspiratory Positive Airway Pressure.
The present invention is directed towards an alternative method and apparatus for resolving upper airway obstruction, resistance or instability.